Process of producing increased yields of tar-free carbon black



July 26, 1955 M. R. CINESI ET AL PROCESS OF PRODUCING INCREASED YIELDSOF TAR-FREE CARBON BLACK 2 Sheets-Sheet 1 Filed Dec. 27, 1949 (OF-F GASFURNACE AIR BLACK CARBON BLACK PROCESS TARRY, UNACCEPTABLE CARBON BLACKIN IN- CREASED YIELD PER UNIT OF FEED ms ma c O UR DD.

INCREASED YIELD OF ACCEPTABLE TAR-'FREE CARBON BLACK PER UNIT OF FEED VI F HIGHER RATE OF FEED THAN USUAL INVENTORJ M. RCINES J. c KREJCIATTORNEYS PROESS OF PRODUCING INCREASED YIELDS 0F TAR-FREE CARBQN BLACKMartin R..Cines, Bartlesviile, Okla, and Joseph C. Krejci, Phillips,Tern, assignors to Phillips Petroleum Company, a corporation of DelawareApplication December 27, 1949, Serial No. 1325,1184

14 Claims. (Cl. 23.-2il9.4)

This invention relates to the production of carbon black. In onespecific aspect it relates to the production of tar-free carbon black inan increased yield per unit of hydrocarbon feed, and per furnace, byproducing larger quantities of tarry carbon black than the maximumpossible production of tar-free carbon black and then detarring thetarry carbon black to produce said tar-free carbon black. This processis only applicable to the making of carbon black in a furnace in whichan axial stream of hydrocarbon in gaseous form surrounded by a helicallymoving blanket of hot gas is passed axially into 1? a reaction zone,because only in such processes can the amount of hydrocarbon in saidaxial stream be greatly increased without such deposit of carbonoccurring, or without the flame being extinguished in the furnace, sothat only in these processes is enough tarry carbon black produced toresult in an increased yield per unit of hydrocarbon feed, and perfurnace, after said tarry carbon black has been detarred.

Such carbon black processes are disclosed and claimed broadly in apatentto Joseph W. Ayers Re. 22,886 of f.-

June 3, 1947. The helically moving blanket of hot gas may be formed byinjecting air tangentially into a cylindrical furnace containing anaxially moving stream of hydrocarbons in gaseous form, whichhydrocarbons may be vaporized liquids or gases, the heat being suppliedby the burning of a portion of the axially moving hydrocarbons.Alternatively air and fuel may be injected tangentially and burned toform the hot helical blanket, or air and fuel may be burned and the hotcombustion gases injected tangentially. Pure oxygen, or otherfree-oxygen containing gas can be substituted for the air. Such specificprocesses are disclosed in Application No. 577,180 filed April 29, 1945(now abandoned) and Application No. 743,893 filed April 25, 1947 byJoseph C. Krejci now U. S. Patent 2,564,700, August 21, 1951.

Since making the present invention our attention has been directed tothe patent to George L. Heller and Carl W. Snow 2,238,576 of April 15,1941, which patent states (on page 1, col. 2, lines 19 to 31) that ahigh yield of carbon black is produced by incomplete combustion ofnatural gas in a plurality of alternate thin wide contacting sheets ofburning gas and air forming thin viscous flame fronts which flames moveforwardly through the combustion chamber in parallel streamlinenon-turbulent relation, and which states (on page 4, col. 1, lines 51 to77) that the quality of the carbon black is protected by producing asolid hydrocarbon black having an acetone extractable content preferablyin the range of 2 to 5 per cent but Without claiming any increase in theyield of carbon black per unit of hydrocarbon feed, or per furnace. Onpage 6, col. 1, lines 53 to 69 Heller states that he can remove thetarry substances with hot acetone, or by prolonging heat treatment ifdesired, but because of the nature of Hellers process there could be noincreased yield of tar-free carbon black per unit of hydrocarbon feed,or per furnace, because the velocity of gas and air in the combustionchamber must average four- 2,7l4fi55 Patented July 28, 1955 teen feetper second, as stated on page 3, col. 2, last paragraph, and it isimpossible to greatly increase the amount of hydrocarbon entering saidfurnace without creating turbulence and destroying the streamline fiowand thin viscous flame fronts; with resulting excessive carbon depositsin said reaction zone and blowing of the flames out of said reactionzone, said flames thereby becoming extinguished and the furnace renderedinoperative.

In contrast in the present process the axial stream of hydrocarbon ingaseous form and the surrounding helically moving blanket of hot gas areboth moving at such velocity (over 100 feet per second) so that theirflow is turbulent and any flames in the furnace are turbulent andviolent in nature as contrasted to the viscous streamline laminar flamesin Heller, so that in the present process the rate of feeding the axialstream of hydrocarbon can be greatly increased without disturbing theprocess except that the carbon black produced will contain an excessiveamount of tar but will be produced in such quantity that after it hasbeen detarred more tar-free carbon black has been produced per unit ofhydrocarbon feed and per furnace.

Furthermore, we unexpectedly obtain greatly increased yields of tar-freecarbon black per unit of hydrocarbon feed and also per furnace by use ofthe present process.

One object of this invention is to produce an increased yield oftar-free carbon black per unit of hydrocarbon yield.

Another object is to produce an increased yield of tarfree carbon blackper furnace.

Another object is to produce carbon black having qualities desirable incompounding with a rubber selected from the group comprising naturalrubber, and rubbery polymers obtained by polymerizing a conjugateddiene.

Numerous other objects and advantages will be apparent to those skilledin the art upon reading the accompanying specification, claims anddrawings.

In the drawings:

Figure 1 is a flow chart showing the relationship of the steps of theprocess.

Figure 2 is a schematic diagram with the parts shown by conventionalsymbols of a carbon black producing plant embodying the presentinvention.

Figure 3 is a fragmentary cross sectional view of the inlet portion ofone form of carbon black furnace suitable for use in Figure 2 incarrying out the invention.

Figure 4 is a cross sectional view of Figure 3 taken along the plane ofpipes 22, looking downstream into reduced diameter zone 28.

As shown in Figure 1, the present invention comprises a furnace blackcarbon black producing process which is operative with air and at ahigher rate of feed than usual, which process produces a tarryunacceptable carbon black in increased yield per unit of feed. The tarrycarbon black is detarred with a resultant increased yield of acceptabletar-free carbon black per unit of feed and per furnace.

In Figure 2 suitable apparatus is shown for carrying out the processoutlined in Figure 1. In Figure 2 the process will be described withrelation to the use of oil as the axial hydrocarbon, and the use of amixture of burning air and gas added tangentially and forming combustiongases in a carbon black furnace having the construction shown in Figures3 and 4 to form the helically moving blanket of hot gas; but this isdone merely for purposes of illustration, and other hydrocarbons ingaseous form surrounded by a helically moving blanket of hot gas,however the same may be produced, can be used in the practice of thepresent invention.

In Figure 2 oil from storage tank 11 is pumped by pump 12 through heater13 where it is heated to such a temperature that when it passes throughpressure reduc- 3 ing valve 14 it is introduced into carbon blackfurnace 16 in the form of an axial stream of hydrocarbon in gaseousform. At the same time fuel, which may be liquid or powdered fuel(because the fuel merely supplies heat and does not generally turn intocarbon black in this process, but which fuel preferably is gas 17), ispumped by pump 13 along with a sufficient amount of air 19 pumped bypump 21 tangentially into furnace 16 through pipe 22. As shown inFigures 3 and 4, the gas from pipe 23 mixes with the air from pipe 24and burns as it emerges from tangentially directed pipe 22 in tunnels 26and/or in the enlarged cylindrical bore 27 of furnace 16, preferably sothat the gas from pipe 23 is completely combusted before the resultinghot combustion gases which spiral inwardly toward the axis of chamber 27contact the axial stream of hydrocarbon from 32. Then said spirallinghot gases pass as a helical blanket down cylindrical bore 28 as a sheatharound the axially moving vaporized oil from heater 13 which is enteringfurnace 16 through axially disposed pipe 29,

which vaporized oil passes centrally through the rotating gas.

In the illustrative example shown in the drawing, oil 11 is preferably agas oil in the neighborhood of 18 A. P. I. gravity comprising aromatichydrocarbons to the extent that said gas oil has an aniline number ofless than 150 F. (and the lower the aniline number the better), gas 17is more than 50 per cent methane, and possibly more than 85 per centmethane, while ordinary air is used at 19, but the scope of theinvention is not limited thereto, as any hydrocarbon in gaseous form canbe used as the axial stream injected in 29, and air alone, orfree-oxygen containing gas, or mixtures of the same with any fluid fuelof a liquid, gaseous, or of granular nature, may be injected in 22 toform the helical blanket of hot gas around said axial stream in thefurnace 16, and the furnace may have other interior configurations (notshown),

'for example, the cylindrical portion 27 may extend the full length ofthe furnace without having any reduced diameter portion 28, or there maybe an orifice of a number of different shapes or sizes restricting aportion of the furnace chamber 27 without departing from the presentinvention. In practice the addition of some air (or other free-oxygencontaining gas) through pipe 31 to an annular space 32 surrounding pipe29 is found to have value in preventing deposition of carbon on the endto tube 29, but it is not essential. The amount of such air can bevaried by adjusting valve 33, or it can be shut off thereby.

By closing valve 34 and opening valve 36 the fuel supplied through line23 becomes oil 11 instead of gas 17, while by opening 36 and 34 andclosing valve 14 the axial hydrocarbon 29 can be shifted to gas. Byproper adjustment of the pressures of pumps 12 and 18 and the positionof valves 14, 34 and 36, a mixture of gas and oil may be employed asaxial stream 29. When oil is employed as fuel in line 22 it need not bethe same quality as that employed as carbon black feed stock in line 29.Whatever fuel is employed in line 23 can be supplied through valve 37 toburner 38 to supply heat for heater 13. By closing valve 39 the materialinjected through line 22 may be limited entirely to a free-oxygencontaining gas such as air.

The axial stream of hydrocarbons in gaseous form passing into thereaction zone of carbon black furnace 16 surrounded by a helicallymoving blanket of hot gas is subjected to pyrochemical reaction by theheat of the surrounding blanket of gas so that a portion of thehydrocarbon is converted to carbon black which carbon black forms assuspended particles in the resulting gases. These resulting gases arecooled by any suitable means in the art, such as indirect heat exchangewater jacket cooling 41, internal quench, water spray, cooling 42 and/orindirect heat exchange air cooling 43. The particles of carbon black areseparated from the off-gas 44 in any suitable means to separate solidsfrom gases 46. In large scale commercial operations in plants havingdozens of furnaces 16, separator 46 generally comprises an electricalprecipitator and some cyclone separators in series in the order named,however bag filter means and a number of other well known separatingmeans can be used instead which reduces the investment if the plant hasfew furnaces. The separated carbon black emerges from the bottom of theseparator 46 through pipe 47. For purposes of conventionalrepresentation separator 46 is shown in the form of a cyclone separatorhaving tangential introduction pipe 48, but unless the cyclone separatoris carefully chosen as to size, it generally will not alone separate outall of the finer carbon black. However if an electrical precipitator isemployed first, the smaller particles will be gathered together intolarger particles by the electrostatic charges received in theprecipitator, which larger particles can be separated very easily byalmost any type of cyclone separator.

In order to make as much of the flow in the drawing go from left toright, so that the drawing is easier to read, a long screw conveyor 49is shown for shifting the compound black 47 to the left in the drawing,but actually screw conveyor 49 is not necessary from a processstandpoint.

The process is operated with a greatly increased amount of hydrocarbonin axial stream 29 over that which will make tar-free carbon black infurnace 16, so that as a result carbon black 47 is tarry, and it isnecessary to deter the same. The remainder of Figure 2 is devoted tosuitable apparatus and processes for producing a tarfree carbon blackacceptable to the rubber industry for compounding with a rubber selectedfrom the group comprising natural rubber, and rubbery polymer obtainedby polymerizing a conjugated diene, characterized by the fact that astandard chloroform extract of tar from said carbon black will transmitat least 85 per cent as much light as a chloroform sample used in theextraction will before making the extraction.

The term rubbery polymer obtained by polymerizing a conjugated diene asemployed in this specification is intended to cover polymers ofbutadiene, piperylene, isoprene, chloroprene, alone or with one or moreof each other, and in some instances with comonomers polymerizabletherewith such as styrene, acrylonitrile and the like, and thesepolymers may contain minor but effective amounts of methyl methacrylateand the like to stiffen the same, but these polymers are all rubbery innature.

For the purpose of the present specification the standard chloroformextract of tar from said carbon black is obtained in the followingmanner:

The tar content of carbon black is determined by mixing 2 grams of blackwith 50 cc. of chloroform, boiling the mixture, filtering, anddetermining the percentage light transmittance of the filtrate ascompared with the transmittance of a blank sample of chloroform. Thecomparison is preferably conducted with a photoelectric colorimeter suchas a Lumetron colorimeter at a wave length of 440 mu, a light intensityof 20, and a cell 1 cm. long. A tar-free black is arbitrarily defined asone that shows a transmittance greater than 85 per. cent according tothis procedure. Most commercial product specifications are more or lessarbitrary, and this one is no exception. Acetone is sometimessubstituted for chloroform in the test procedure. The per centtransmittance equivalent to 85% with chloroform is about 92% withacetone. The original acetone or chloroform used for the test should besubstantially colorless.

The tar content of a carbon black depends on the temperature and thereaction time at' which the black is produced. At a constanttemperature, tar content increases as reaction time decreases. At aconstant reaction time, tar content decreases as temperature increases.Temperature and reaction time are inter-dependent in this respect. Thespecific temperature and the specific reaction time in any specific casewill depend on furnace design, on the chemical properties of the feed,on the fuel-air mixture used, and on the ratio of axial to tangentialfeed. Specific data for obtaining tarry black and tar-free black from acertain feed and in a certain furnace are given in examples below. For agiven feed, a given furnace, a given tangential fuel-air mixture, and agiven feed rate for the fuel-air mixture, increasing the oil feed rateabove a certain value will decrease the reaction time and thetemperature and increase the tar content and the yield of carbon black.As the oil feed rate is increased further, a value will be reached atwhich the carbon black yield will decrease and production of crackedhydrocarbons will become increasingly evident. The specific conditionsfor this maximum yield of carbon black will vary in accordance with theconditions previously discussed.

It is believed that one skilled in the art can, by applying theprinciples and the test method discussed in the preceding paragraphs,readily produce an increased yield of tarry carbon black from any givenfeed with any given apparatus.

The tarry carbon black moving down screw conveyor 49 is removed at 51 byoperating valve 52 if it is desired to produce a more or less flocculentblack as a product, but in a number of cases it is desired to produce apelleted black and therefore valve 52 is closed and the tarry black 47moves to the end of conveyor 49 and emerges through pipe 53 controlledby valve 54 into the screw conveyor 1;.

56 of pelleting drum 57. Considerable difficulty in pelleting some kindsof tarry black may be experienced unless the pelleting process disclosedby Merton Studebaker in application Serial No. 589,811, filed April 23,1945,

now U. S. Patent 2,503,361 April 11, 1950, is followed 2:.

in drum 57. Other tarry blacks pellet by mere one trip passage throughthe drum.

Briefly in said pelleting process drum 57 rotates and is about to fullof a mixture of pellets and flocculent black in the form of a bed. Drum57 is smooth and cylindrical and as it rotates, part of the mixture iscarried up on one side of the drum by friction until the angle of reposeof the carbon black mixture therein is exceeded whereupon the carbonblack cascades and tumbles with a rolling motion down and across the bedto the low side of the bed. Pellets are preferably constantly withdrawnthrough chute 58 and all are passed through screen 59 which is merely toremove mill scale and occasional large masses of solidified carbon blackinto a trash bin 61. All sizes of pellets go through screen 59 intohopper 62 where a desired proportion of the pellets are preferablyrecycled by adjusting valve 63 so that they may be carried back by belt64 into feeding means 56. With some carbon blacks the recycle can beeliminated by closing valve 63.

At the same time a proportion of finished pellets pass through pipe 66onto belt 67 into hopper 68. Hopper 68 also is adapted to receiveflocculent carbon black 51 when valve 52 is open, with any desiredamount of pellets from 67 or without any pellets when valve 54 isclosed. Whether the feed in hopper 68 is straight pellets from 67 orstraight flocculent carbon black from 51 or a mixture from both does notchange the operation of the tar removing treatment which will now bediscussed.

We have now discovered that large enough percentages (by weight) of tarcan be removed from carbon black to make a suitable tar removal processfor use with the present invention, by employing the same processeswhich were developed for decreasing the pH, increasing the scorch time,and/ or hardening carbon black pellets and are described in applicationSerial Nos. 67,674 filed December 28, 1948 and 87,473 filed April 14,1949 by Martin R. Cines now U. S. Patents 2,682,448 June 29, 1954 and2,641,535 June 9, 1953, respectively. The process of No. 67,674 gives amore complete removal of tar than that of No. 87,473, but in many casesthe later process gives sufficient tar removal for the purposes forwhich the car'- bon black is being made. As these two processes arefully described in said two applications a brief description will besulficient in the present application.

It is entirely possible from a commercial standpoint to detar carbonblack with chloroform or acetone as suggested by Heller 2,238,576patented April 15, 1941, but the gas treatments briefly described hereinare much cheaper and generally much more satisfactory, because the taris actually converted to carbon black to a large extent instead of beingremoved by a solvent, and the problem of extracting the tar from theliquid solvent is thereby obviated while the yield is slightlyincreased. However, the large increase in yield in the present processis not due to this minor increase caused by using gas, as tests in whichthe tar was removed by chloroform or acetone clearly will show thatthere is a substantial and unexplained increase in the amount of carbonblack produced regardless of how the tar is extracted.

In Figure 2 the carbon black from hopper 68 passes through a rotatingstar wheel air lock 69 of conventional design and through a motor drivenscrew feed 71 into a treating drum 72. Drum 72 is rotated by motor 73driving shaft 74 and wheel 76 which engage drum 72 by frictional contact(and the same means is used to rotate the pellet drum 57 and theflushing drum 77). After the carbon black has spent a minimum averagetime in the treating drum 72 it is discharged through suitable starvalves into drum 77 where the treating agent may be flushed out by air,inert gas, or a secondary gas treating agent from line 78. However, inmany instances, especially when air is used as the primary treatingagent in treating drum 72, it is only necessary to draw off the carbonblack through pipe 79 controlled by valve 81, while valve 83 is closedand stationary. Obviously if the temperature in treating drum 72 isabove the ignition temperature for the carbon black in the open air,then pipe 79 should be long enough and small enough in diameter toprovide sufficient air cooling so that the carbon black going intoproduct bin (A)82 will not catch fire,

and obviously some form of heat exchange such as a water jacket (notshown) can be provided for cooling the carbon black in pipe 79 below theair ignition temperature.

When valve 81 is opened, valve 83 is stationary, but if it is desired toflush the product and place the same in product bin (8)84 then valve 81is closed and star valve 83 is rotated.

As drums 72 and 77 rotate gases are passed through the same. Thesimplest treatment involves taking air from 86, pumping it at 87,heating it at 88 to a temperature ranging from 400 F. to 1200 F. Thepreferred temperature range is from 600 F. to 1000 F. The air so heatedin heater 8% passes through pipe 89, drum 72 and out the exhaust 91. insuch a treatment the average time of the pellets in the treating drum 72should be in the neighborhood of one hour.

While it is possible under excellent heat transfer conditions to operatewith undiluted air at these elevated temperatures, under normalconditions an excessive amount of carbon black is lost through oxidationespecially at the higher temperature. For such elevated temperatures itis better to operate with diluted air having an oxygen content between2.5 and 5 per cent which can be obtained by recycling the oxygendepleted air in 91 to the desired extent through pipe 92 which isaccomplished by pump 95 and by adjusting valves 93 and 94. At the sametime the gas recycle can be preheated to the desired amount and used asa temperature control by adjusting valves 96 and 97 to recycle as muchas desired through heater 88. Furthermore, by adjusting valves 98 and 99and the pressure of pump 100 the amount of new air added and the amountwhich it is preheated can be regulated.

With such a treatment it is merely necessary to cool the carbon black inpipe 79 below the ignition temperature, but if it is desired to be surethat further oxidation is completely prevented the carbon black withsufficient cooling (not shown between 72 and 77) is passed into flushingdrum 77 and flushed out with an inert gas such as nitrogen, carbondioxide, or perhaps hydrogen, or even air at a low enough temperature tobe substantially inert, which inert gas may be exhausted through valve101 or recycled through valves 102 or 105 or both, to the degreedepending on the adjustment of the respective valves. Cooling can alsooccur by radiation of heat from drums 57, 72, and 77, and inert gas 78can be a cooling agent in drum 77.

In order to decrease the time of treatment and to operate at aconsiderably lower temperature it is often desirable to add a suitableoxidation catalyst, sulfur dioxide being greatly preferred. Thesebenefits are attained at some sacrifice of tar removal and are thereforeattainable only in those cases where greater tar content can betolerated. The sulfur dioxide is added preferably as a vapor from tank103 through valve 104 during the same operations already described tothe amount of 0.1 to volume per cent of sulfur dioxide in the stream 89.Optimum results are obtained with 0.5 to 1.5 volume per cent of sulfurdioxide. It is necessary however that some air or other free-oxygencontaining gas be added at 36 and although greater or smaller amountsmay be used I prefer to use 5 to 50 cubic feet of air per pound of blackand to maintain contact between the black and air for a sufiicient timeto attain the desired detarring which may occur in as little time as tenminutes to one hour as the average time the carbon black is in drum 72although treating times outside this range may be used. The desiredeffects are obtained with sulfur dioxide additions at temperaturesbetween 300 F. and 400 F. The maximum tar removal with SOz-air treatmentat 350-400 F. produces a photometric value of 82.

While Figure 2 shows a pellet drum 57 separate from the treating drum72, obviously the two can be combined in one. For example by closingvalve 54 and opening valve 52, operations in drum 72 can either bedetarring of flocculent carbon black, or, by speeding up the rotation ofdrum 72, increasing the time the carbon black spends in the drum, and/orby adding a recycle (not shown) like 64, partial, or complete pelletingof the carbon black can be accomplished at the same time as the carbonblack is being detarred. When drum 72 is heated above 300 F. the recyclesystem (not shown) becomes quite complex, as to minimize loss of carbonblack due to oxidation the recycle (not shown) should be a systementirely enclosed from the atmosphere and preferably taking the carbonblack from pipe 79 above valve 81 and carrying the same by an enclosedbelt like 64 to an enclosed connection (not shown) to the pipe belowstar valve 69.

In either the sulfur dioxide or straight air methods described above theair 86 can be modified by the addition of other gases such as oxygen,nitrogen, and/or the recycled gases in pipe )2 without departing fromthe invention.

EXAMPLE A Carbon black was produced by pyrochemical reaction asdescribed above of an 18 A. P. I. gravity gas oil in a cylindricalfurnace without any enlarged section at a reaction temperature in therange of 2400-2700 F. The furnace was 9% inches'in diameter and 46inches long. It was provided with three tangential inlets for air and aone-half inch axial inlet for oil. The one-half inch oil inlet wasjacketed with a one-inch pipe for introduction of air to prevent cokedeposition on the oil inlet. The oil was preheated and vaporized at 700F. before introduction into the furnace. The effluent from the furnacewas passed into conventional cooling and recovery equipment forcollection of the carbon black product. The data obtained are shown inthe following tabulation:

A sample of the carbon black produced in each of the two runs wasextracted with chloroform. The chloroform extract from the carbon blackof run B621 was colorless, indicating that the carbon black containedsubstantially no tar. The chloroform extract from the carbon black ofrun B625R was yellow, indicating an appreciable tar content; in fact,the tar content was above the maximum commercial specification asdefined above of at least 85% light transmission.

The carbon blacks from both runs are separately treated with a gasconsisting of 97 volume per cent nitrogen and 3 volume per cent oxygen.The gas flows upward through a fluidized bed of the carbon black at therate of 59 cubic feet per pound of carbon black per hour. The followingdata are obtained:

From calculations based on Table I and Table II it is apparent that runB621 produced low-pH, specification carbon black at the rate of 117pounds per hour, whereas run B625R (this invention) produced a similarproduct at the rate of 152 pounds per hour. This is an increase of 30per cent in production for a 19 per cent increase in oil feed rate. Thetreated black from run B625R (pH=6.0) is tar-free. Furthermore atemperature of 840 F. is required to reduce the pH of the black from runB621 from 9.6 to 6.0 in one hour, whereas a lower temperature (300)produces a comparable pH decrease with the black from run B625R (thisinvention) in the same time. Also, the oxidation loss is lower in run8625 R.

EXAMPLE B It is known that present carbon black operations are adjustedto yield an essentially tar-free product. It is also known that thethroughput of the furnaces could be increased, increasing the yield ofblack per gallon of feed, without interfering with the operation of thefurnace. However, the resulting product from this increased feed rate isnot acceptable because of excessive residual tars. It has been shownthat by high temperature (800-900" F.) oxidation of the surface ofcarbon blacks, various physical properties of the black can be modified.In the course of the oxidation studies, it was also established that allresidual tars, as determined by chloroform extraction tests, weredestroyed.

This'invention consists of a process in which the carbon black furnaceis operated at the maximum feed rate consistent with maintaining thefurnace Walls free of carbon deposits. The product from the furnaces arethen subjected to an oxidative after-treatment with air at temperaturesbetween 600-900 F. in which the residual tars are destroyed. Inaddition, the surface complex of the black is increased and the pHlowered.

The oxidation treatment may be carried out at lower temperatures thansurface oxidation treatments for tarfree blacks. The following data on atarry black (P-l) prepared at 210 gal./hour feed rate by the pilot plantat the Philtex Experiment Station show the tar removal as a function oftemperature. The tangential air rate was 9 125,000 cublic feet air/hour,and the rate of the tangential gas was 8300 C. F. H.

Table III DE-TARRING OF CARBON BLACK OF EXAMPLE B Percent Contact H Air3 Fieed, .2 5 Pelr cent Run Tem Time, p ,1 at

p Min. #Black gsifgf Removed Cell 47 0 64 56 6 12a 56 6 32 59 14 64 6564 79 at 86 3352-P-180 a 5. 3 b 100 b 100 a Run in glass kiln. otherdata are from small glass circulating bed apparatus. b Estimatedbased onstatement that chloroform extract was water wn'te.

As an example of the effect of de-tarring by oxidation Table VII onoverall plant operations, the following data from pilot lant o erationsare presented: v Treating Tar p P Run No. Percent Time, $3 52 Temp. pHii fi i Re- Table IV S02 Hrs. g moved 3513-34- 2.5 1.0 33.9 305 3.8 6.164 Date 3555 3513---- 1.14 1.0 34.7 355 3.3 81.1 72

$ 31??? l i 3 2g *44 m fi t r, 10 mm. rectangular cell, light intensityof 20.

1e 5. ga v I, i Totalproductivity,lbsJhr 590 vt heieas 1n the laminarviscous flame method of sa1d pH of product 9. g Heller Patent 2,238,5761t 1s necessary that the absolute Scorch time, min a DH after treatment(20 jn jr ggf velocity of g pas d thiough the combustion Zone shallin...- average in the nelghborhood of 14 feet per second and Scorch timeafter treatment, 111

The de-tarring step does not cause any appreciable loss in yield.

It will be seen from Table IV that an increase of 15.3 per cent in thefeed rate of gas oil results in an increase of 34.1 per cent in theyield of carbon black in pounds per hour per furnace, and at the sametime the yield in pounds of carbon black per gallon of oil feed wentfrom 3.3 pounds per gallon to 3.8 pounds per gallon, an increase of 15per cent per unit of hydrocarbon feed.

EXAMPLE C The following Tables V, VI and VII show further the beneficialeffects of the present invention. The pH of the carbon black has arelation to the time of scorch as a carbon black with a high pH cannotbe worked very long without scorching the same.

Table V Max. oil rateffor CB Talgig.t Air R t t u .tced tarree a e, Airgas a 10 a g product, o. F. H.

G. P. H.

Table VI Color of Tang. air Air-gas Ratio tang. a CB, Rate,

Fee on rate 1bS-/ga1- o. F. H.

*Predicted maximum possible oil rate (not tested).

can not be varied by any substantial amount, in contrast, in the presentprocess, the hydrocarbon in gaseous form passing axially through thefurnace moves several hundred feet a second in the production oftar-free carbon black and this velocity is greatly increased inproducing increased quantities of tarry black. While the exact velocitywill vary somewhat according to the air rate, gas rate (if fuel gas isemployed tangentially) the type of black being produced, the type ofhydrocarbon (such as gas oil or gas) being passed axially through thefurnace and the reactor dimensions, the velocity of the axially movinghydrocarbon is in the range of several hundred feet a second. However,it is easy for the operator to increase the axial feed of hydrocarbonsuntil a tarry black is produced, and this does not requireexperimentation.

EXAMPLE D For example, in a furnace of the type shown in the presentdrawings having a l2-inch diameter reaction section 28, which is 11 feetlong, and using as tangential feed through pipe 22 about 125,000 cubicfeet of air per hour and 8,300 cubic feet of gas per hour with an axialfeed through pipe 29 of gallons per hour of 100 F. aniline number gasoil, a tar-free black was produced. Up'on increasing the axial feed to210 gallons per hour an increased yield of tarry carbon black per unitof feed and per furnace was produced in such quantity as to reduce thecost of producing a final tar-free carbon black from about one-fourth toone-half cents a pound even after the added expense (includingadditional plant equipment) of detarring the carbon black was added tothe cost of the product.

It is impractical to give exact limits but the operator of the furnacecan easily vary the conditions and produce a tarry black in increasedyield and still not increase the axial'feed of hydrocarbon to such apoint that the furnace becomes too rapidly clogged by carbon deposits.Even atmospheric conditions affect the operation of the furnace and itis common operating practice to observe furnace operating conditionsfrom time to time and to make corresponding adjustments withoutinvention as such is within the skill of the ordinary furnace operator.

While specific examples have been given and specific apparatus has beenshown, these have been disclosed for purposes of illustration of theinvention, and the best mode of practicing the same, and should not beregarded as limiting the scope of the invention, which is as set forthin the accompanying claims.

Having described our invention, we claim:

1. The process of producing an increased yield of tarfree carbon blackacceptable to the rubber industry for compounding with a rubber selectedfrom the group comprising natural rubber, and rubbery polymers obtainedby polymerizing a conjugated diene, characterized by the fact that astandard chloroform extract of tar from said carbon black will transmitat least 85% as much light as the chloroform used will before theextraction, which comprises the steps of passing an axial stream ofhydrocarbon in gaseous form surrounded by a helically moving blanket ofhot gas into a reaction zone, which blanket of hot gas forms carbonblack in said axial stream by pyrochemical reactions, and which hotblanket permits the amount of hydrocarbon in said axial stream to begreatly increased without substantial carbon deposits in said reactionzone, feeding said hydrocarbon into said reaction zone at a rate higherthan that which will produce a maximum yield of said tar-free carbonblack and said rate being so high that an increased yield of tarryunacceptable carbon black having an alkaline pH, the standard chloroformextract from which has less than 80% light transmission than saidchloroform is produced over the amount of tar-free carbon black thatcould be produced in said reaction zone from the same weight of saidhydrocarbon cooling said tarry black, and detarring and re ducing the pHof said tarry carbon black by intimate mixing with, and exposure to, anoxidizing gas comprising free oxygen under an oxidizing temperature or"from 400 F. to 1200 F. to produce said tar-free carbon black the lighttransmission of a standard chloroform extract of which is at least 85%of said chloroform in an increased yield per unit of hydrocarbon feedand per reaction zone over the yield of said tar-free carbon black thatcould be produced from said feed in said reaction zone.

2. The combination of claim 1 in which the axial stream of hydrocarboncomprises over 50 per cent of a gas oil comprising aromatic hydrocarbonsto the extent of having an aniline number less than 150 F.

3. The combination of claim 2 in which the helically moving blanket ofhot gas is formed by the complete combustion of a gas comprising over 50per cent methane with air before contacting said axial stream.

4. The combination of claim 1 in which the axial stream of hydrocarboncomprises over 50 per cent of a gas oil having an aniline number of lessthan 150 F. and the helically moving blanket of hot gas is formed bycombustion of a portion of the axial stream in air injected tangentiallyinto said reaction zone.

5. The combination of claim 1 in which at least part of the detarring ofthe carbon black is by exposure to an oxidizing gas containing from 0.1to 5 volume per cent of sulfur dioxide at a temperature between 300 F.and 400 F. and the loss of carbon black during detarring is less than 5per cent.

6. A process of producing an increased yield of tarfree carbon black,characterized by the fact that a standard chloroform extract of tar fromsaid carbon black will transmit at least 85% as much light as thechloroform used will before the extraction, which comprises the steps ofpassing an axial stream of hydrocarbon in gaseous form surrounded by ahelically moving blanket of hot gas into a reaction zone, which blanketof hot gas forms carbon black in said axial stream by pyrochemicalreactions, and which hot blanket permits the amount of hydrocarbon insaid axial stream to be greatly increased without substantial carbondeposits in said reaction zone, feeding said hydrocarbon into saidreaction zone at a rate higher than that which will produce a maximumyield of said tar-free carbon black and said rate being so high that anincreased yield of tarry unacceptable carbon black the standardchloroform extract from which has less than 80% light transmission thansaid chloroform is produced over the amount of tar-free carbon blackthat could be produced in said reaction zone from the same weight ofsaid hydrocarbon, and detarring said tarry carbon black to produce saidtar-free carbon black in an increased yield per unit of hydrocarbon feedper reaction zone.

7. A process according to claim 6, in which the axial stream ofhydrocarbon comprises over 50 per cent of a gas oil comprising aromatichydrocarbons to the extent of having an aniline number less than 150 F.

8. A process according to claim 6, in which the helically moving blanketof hot gas is formed by the complete combustion of a gas comprising over50 per cent methane with air before contacting said axial stream.

9. A process according to claim 6, in which the helically moving blanketof hot gas is formed by combustion of a portion of the axial stream inair injected tangentially into said reaction zone.

10. A process according to claim 6, in which an axial stream ofvaporized gas oil surrounded by a helically moving blanket of hotcombustion gas is passed into the reaction zone.

11. A process according to claim 10, in which the hot combustion gas isproduced by completely burning a fuel in air before contact with saidaxial stream.

12. A process according to claim 10, in which the hot combustion gas isformed in the reaction zone by burning a portion of said axial streamwith air injected tangentially into said reaction zone.

13. A process according to claim 6, in which the detarring of the carbonblack is by exposure to an oxidizing gas under oxidizing temperatureconditions and the loss of carbon black during detarring is less thanthe gain in carbon black from making tarry carbon black instead oftar-free carbon black.

14. The process according to claim 6, in which at least part of thedetarring of the carbon black is by exposure to an oxidizing gascontaining from 0.1 to 5 volume per cent of sulfur dioxide underoxidizing temperature conditions and the loss of carbon black duringdetarring is less than 5 per cent.

References Cited in the file of this patent UNITED STATES PATENTS Re.22,886 Ayers June 3, 1947 1,285,363 Pike Nov. 19, 1918 2,238,576 Helleret a1 Apr. 15, 1941 2,342,862 Hemminger Feb. 29, 1944 2,375,795 KrejciMay 15, 1945 2,393,106 Johnson et a1. Jan. 15, 1946 2,587,107 Cade Feb.26, 1952 FOREIGN PATENTS 83 Great Britain of 1886

1. THE PROCESS OF PRODUCING AN INCREASED YIELD OF TARFREE CARBON BLACKACCEPTABLE TO THE RUBBER INDUSTRY FOR COMPOUNDING WITH A RUBBER SELECTEDFROM THE GROUP COMPRISING NATURAL RUBBER, AND RUBBERY POLYMERS OBTAINEDBY POLYMERIZING A CONJUGATED DIENE, CHARACTERIZED BY THE FACT THAT ASTANDARD CHLOROFORM EXTRACT OF TAR FROM SAID CARBON BLACK WILL TRANSMITAT LEAST 85% AS MUCH LIGHT AS THE CHLOROFORM USED WILL BEFORE THEEXTRACTION, WHICH COMPRISES THE STEPS OF PASSING AN AXIAL STREAM BYCARBON IN GASEOUS FORM SURROUNDED BY A HELICALLY MOVING BLANKET OF HOTGAS INTO A REACTION ZONE, WHICH BLANKET OF HOT GAS FORMS CARBON BLACK INSAID AXIAL STREAM BY PYROCHEMICAL REACTIONS, AND WHICH HOT BLANKETPERMITS THE AMOUNT OF HYDROCARBON IN SAID AXIAL STREAM TO BE GREATLYINCREASED WITHOUT SUBSTANTIAL CARBON DEPOSITS IN SAID REACTION ZONE,FEEDING SAID HYDROCARBON INTO SAID REACTION ZONE AT A RATE HIGHER THANTHAT WHICH WILL PRODUCE A MAXIMIUM YIELD OF SAID TAR-FREE CARBON BLACKAND SAID RATE BEING SO HIGH THAT AN INCREASED YIELD OF TARRYUNACCEPTABLE CARBON BLACK HAVING AN ALKALINE PH, THE STANDARD CHLOROFORMEXTRACTED FROM WHICH HAS LESS THAN 80% LIGHT TRANSMISSION THAN SAIDCHLOROFORM IS PRODUCED OVER THE AMOUNT OF TAR-FREE CARBON BLACK THATCOULD BE PRODUCED IN SAID REACTION ZONE FROM THE SAME WEIGHT OF SAIDHYDROCARBON COOLING SAID TARRY BLACK, AND DETARRING AND REDUCTING THE PHOF SAID TARRY CARBON BLACK BY INTIMATE MIXING WITH, AND EXPOSURE TO, ANOXIDIZING GAS COMPRISING FREE OXYGEN UNDER AN OXIDIZING TEMPERATURE OFFROM 400* F. TO 1200*F. TO PRODUCE SAID TAR-FREE CARBON BLACK THE LIGHTTRANSMISSION OF A STANDARD CHLOROFORM EXTRACT OF WHICH IS AT LEAST 85%OF SAID CHLOROFORM IN AN INCREASED YIELD PER UNIT OF HYDROCARBON FEEDAND PER REACTION ZONE OVER THE YIELD OF SAID TAR-FREE CARBON BLACK THATCOULD BE PRODUCED FROM SAID FEED IN SAID REACTION ZONE.